A conventional set of building blocks include various shapes of wooden blocks which can simply be built up one over another from lower to upper. It is hardly contemplated to place, for example, a triangle block in its inverted form on the horizontal plane. A resultant building of blocks will thus be far from uniqueness.
As disclosed in Japanese Patent Laid-open Publication (Heisei) 11-319333, a modification has been proposed in which each block has four sides equally recessed in the surface thereof. It is however troublesome to fabricate the equally recessed sides of the block. When the recessed blocks are built up one over another, their recessed sides have to join with each other. This joining action is equal to that of the conventional blocks and may give a limitation on the building pattern.
Also, another modification including some blocks provided with V-shaped grooves is disclosed as a building toy in Japanese Patent Laid-open (Showa)56-31783. The blocks are arranged with the V-shaped groove substantially identical in the width to the surface of the other side so that it can neatly engage with the top of a roof block, hence exhibiting no balancing favor nor shaping uniqueness.